Thermoset /thermoform plastics recommendations 1

[screenman]

Hello, I hope someone can give me an idea where to start here. Currently i am using a two part polyurethane thru a gun dispenser to make the parts that i need but am hopeful that there is an easier way to produce.

essentially i am taking a group of parallel, equally spaced carbon or 304 stainless wires , ranging in diameters of 1.6mm to 3.0mm and a spacing of 6mm thru 15mm and pouring a perpendicular polyurethane strip approx 30mm wide by 6mm thick.

The current process works fine from a finished product standpoint, it has the sliding abrasion resistance and flexibility that i require but it is a time consuming and wasteful process.

I was hoping that there was a plastic out there that would provide some of the same characteristics as the two part PU yet would come in a solid state (strip/coil form) and could be activated by a heat lamp or some such device, so I could lay it out and position it and then heat it??? and the wires would sink into it and then when the heat/whatever was removed it would set up and the wire would be covered.

I am not against using two strips, one on the top and one on the bottom of the wire and then have them bond together.

The key thing is the wire is trapped and will not come apart

thanks

 

[patprimmer]

You could injection mould in 2 halves then assemble and ultrasonically weld them together.

Regards

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[patprimmer]

You could even solvent weld some types of thermoplastic together.

Regards

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[screenman]

Thank you Patprimmer. However I need the two pieces, if i go that route, to conform around and completely encapsulate the wire and become one, similar to the polyurethane that I am pouring right now

 

[Theophilus]

The problem with using injection molds is that you've got variable spacing and wire diameters--that could add up to lots of injection tooling (depending on your variations). If you do something like that, using styrene would allow good solvent bonding (and it's inexpensive). However, that may or may not deliver the strength and other characteristics you need.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

Due to some apparent contradictions in your statements, it is becoming quite unclear to me as to what you really want to do.

Are you trying to permanently encapsulate the wires.

Do the sizes vary from piece to piece or is it always the same collection of sizes.

I really don't want to get involved in a drawn out guessing game, but if you clearly tell us what you really want to do, I am sure a few will offer good advice.



Regards

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[screenman]

Thank you Theophilus. you are right, there is a myriad of different combinations and permutations that are possible, so to have moulds made up would be unfeasible.

 

[screenman]

Patprimmer, yes, I am trying to permanently hold the wires in place, and these parts will vary in aperture and wire diameter almost infinitely. I feel, if I go the two part method, then each part will need to melt to meet the other and become one. Presently I am pouring a urethane into a mould which the wires go thru @ right angles. When it sets up, I have a bottom cover and a top cover and the wire in between. I thought that there might be a plastic available that I could lay the wire over the top of and at ambient temperature the wire would remain on top but if I heated it to an elevated temperature, the plastic would soften and the wires would sink into it and the plastic would absorb them, then removing the heat source it, the plastic would return to it original state and the wires would be trapped.
I am not sure that such a plastic exists or if it can be done with heat. Any ideas?
Thanks

 

[Pud]

You mentioned wear resistance in your op - you are not going to get better than 2 part PU for this. All injection moulding materials fall someway short of cast PU in this respect - even inj moulding grades of PU.

imho, you may already have the best solution if not the best manufacturing process.


Cheers

Harry

 

[patprimmer]

To my knowledge there is no thermoplastic that is fluid enough in the melt state to allow the metal to sink under gravity and for the plastic to flow over the top and weld properly.

In injection moulding, pressures from 5000 to 20000 psi are typically necessary to force the plastic to fill the mould and conform to the surface. The forces from gravity are more like 1 or 2 psi, or less than 1 psi at the weld line.

Also, thermoplastics normally degrade when exposed to air for more than a few seconds at their melt temperature.

As others have said, cast polyurethane really does sound like the best process for you. You may be able to speed up the process with different grades, moulds and process conditions.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.